So far, various medical composite materials have been developed to address the problem of wound healing. Man has long searched for proper materials to aid healing and regeneration of tissues or their replacement when the first option fails. Man has borrowed solutions and materials from nature. The first biomaterials used by man were derived from naturally occurring materials such as catgut that has been documented used by old Egyptians. Indians have used various replacement materials. For demanding tissues where mechanical properties are important, i.e. hard tissues for their primary function to keep the frame of the body, cartilage and bone were thus treated mainly with splinting and immobilization. However, this procedure implies the loss of function and disability that, although, temporary, it can lead to complications. When metals were used for fixing bone fractures, it was possible to make patients walk very early and resume function, and thus an “internal” splinting system was introduced. In the recent years research in the area of tissue generation and regeneration has expanded and new principle of treatment has been developed to allow for making grafts in the laboratory. For a body frame-keeping, load bearing system comparable to bone, it has been difficult to develop reliable biomaterials that are biocompatible, temporarily present in the body (elimination by body itself), and mechanically reliable. Such a material that can be used to aid bone repair, regeneration or generation and/or augmentation that can also be used to help osteoconduction is not present up to our knowledge and there is a burning need to develop such a material.
Various materials have been developed to act as scaffolds for bone tissue generation or regeneration. They have been called so because they offer a medium to which cells can attach and can be transplanted (carriers). However, early scaffolds were made of polymers, namely polyesters, polyglycolide, polyglycolide/polylactide and later from polylactide. These polymers as such may not always possess sufficient strength to bear weight and an additional supporting mechanism is needed to help bone in weight-bearing which the function of the scaffold is limited to support the healing of the void, defect or gap with bone regeneration by transplanted cells or tissue grafts such as periosteum.
On the other hand devices based on ceramics alone have also been explored back in the history as filler materials and recently as scaffolds for tissue generation, regeneration or repair. Hydroxyapatite is one example of ceramics that has been studied. However, hydroxyapatite, although biocompatible and osteoconductive, is practically not bioabsorbable and may lead to formation of fibrous tissue at the interface between the bone and the implant. Tricalcium phosphate has been found to be a resorbable ceramic that can be osteoconductive as well. With the current technology, it is however, difficult to manufacture it into fibers. Bioactive glass that can lead to formation of apatite layer at the interface between bone and the ceramic has been used as filler material in some clinical cases. With recent advances, it has been possible to make bioactive glass into fibers. However, these fibers alone are brittle and can not bear the load when used in the skeleton that should bear the weight of the body. There is, thus, an obvious need to develop a reliable, osteoconductive device for treatment of bone and/or cartilage fractures, osteotomies, defects that may follow trauma, congenital deficiencies, disease or surgical resection.
An example of a biocompatible implant is shown in U.S. Pat. No. 5,084,051. The implant is made of biocomposite material comprising at least one bioceramic component layer and at least one material component layer, which has been manufactured of at least one polymer, both components having certain porosity.
U.S. Pat. No. 6,579,533 describes a bioabsorbable drug delivery material comprising synthetic bioabsorbable polymeric matrix, antibiotic and bioactive glass dispersed in the polymeric matrix. The document mentions a possibility to spin drug releasing materials to fibers which can be formed to knitted or woven fabrics for example.
U.S. Pat. No. 5,626,861 is a good example of a conventional technique for obtaining 3-dimensional macroporous polymer matrices for use as bone graft or implant material. Mixing a polymer solution, hydroxyapatite particles and inert particles, which are removed by leaching after the solvent of the polymer has evaporated, forms the composite. The technique requires many processing steps and use of organic solvents. The inner porosity cannot be thoroughly controlled through this procedure.
Publication WO 02/08320 shows a simpler technique avoiding the use of solvents, but it still requires the use of the special “porogen” substance, which must be removed from the composition to create the porosity.
An example of a biocompatible implant for surgical implantation is shown in US published patent application no. 2002/0143403 and corresponding publication WO 02/053105. This implant comprises a matrix of a resorbable thermoplastic-ceramic composition, the matrix having a pore size and porosity effective for enhancing bone growth adjacent the composition. The implant structure is made by using ribbon or filament deposition process. The ribbons or filaments of extruded composition are deposited layer upon layer onto the work or support surface in a predetermined pattern to form an object of desired size and shape and having the desired porosity characteristics, using a special extrusion freeform (EFF) process. One material for the composition is a blend of thermoplastic polymer and calcium phosphate.